What is Second Degree AV Block


It is of 3 types:
• Mobitz type I (Wenckebach’s phenomenon).
• Mobitz type II.
• 2 : 1 or 3 : 1 heart block.

Mobitz Type I (Wenkebach’s Phenomenon)


Progressive prolongation of PR interval followed by a drop beat.

ECG findings

Progressive lengthening of PR interval followed by absent QRS complex.

Site of block

Higher area of AV node (proximal to bundle of His).


• Physiological—in athlete, during rest, sleep (due to increased vagal tone).
• Drugs—digoxin toxicity.
• Acute myocardial infarction (commonly inferior MI).


• Usually, asymptomatic.
• Features of primary disease.


• Pulse is irregular (drop beat occurs).


• No treatment is required.
• Primary cause should be treated.

Mobitz Type II AV block:

Site of lesion

Disease of His-Purkinje system.

ECG Criteria

• Some P waves are not followed by QRS complexes.
• PR interval is constant (also PP interval constant).
• QRS—wide.
(In 2 :1 AV block, alternate P wave is conducted. It may be 3:1, 4:1). This type of AV block is rare and more severe. It is generally a sign of severe conduction system disease.


Acute anterior myocardial infarction.


1. If due to inferior myocardial infarction:
–– If asymptomatic—close monitoring and follow-up.
–– If symptomatic—Injection atropine 0.6 mg IV. If fails, temporary pacemaker. Majority will
resolve in 7–10 days.
2. If due to anterior myocardial infarction—temporary pacing followed by permanent pacemaker
is required (because complete heart block may develop).